U.S. patent application number 13/151431 was filed with the patent office on 2012-03-08 for angular adjustable variable beamsplitter.
Invention is credited to John H. Hunter, Ian J. Miller.
Application Number | 20120057241 13/151431 |
Document ID | / |
Family ID | 45770549 |
Filed Date | 2012-03-08 |
United States Patent
Application |
20120057241 |
Kind Code |
A1 |
Hunter; John H. ; et
al. |
March 8, 2012 |
ANGULAR ADJUSTABLE VARIABLE BEAMSPLITTER
Abstract
A beamsplitter includes a bifurcated frame, which rotates about
a vertical axis, enabling the transmissive properties of an optical
element, e.g. etalon, mounted on one arm of the frame, to be tuned
as the angle of the optical element is rotated relative to an
incoming optical beam. A mirror is mounted on the other arm of the
frame intersecting light reflected from the optical element and
redirecting the reflected light along a path, which is constant
relative to the incoming optical beam.
Inventors: |
Hunter; John H.; (Almonte,
CA) ; Miller; Ian J.; (Ottawa, CA) |
Family ID: |
45770549 |
Appl. No.: |
13/151431 |
Filed: |
June 2, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61380840 |
Sep 8, 2010 |
|
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Current U.S.
Class: |
359/629 |
Current CPC
Class: |
G02B 26/02 20130101;
G02B 7/003 20130101; G02B 7/006 20130101; G02B 26/0816
20130101 |
Class at
Publication: |
359/629 |
International
Class: |
G02B 27/14 20060101
G02B027/14 |
Claims
1. An optical beam splitter comprising: an input port for launching
an input optical signal at a first wavelength along an input path;
a frame rotatable about a rotation axis perpendicular to the input
path; a first arm extending from the frame; an etalon mounted on
the first arm disposed in the input path at a first variable acute
angle of incidence, whereby the input optical signal is split into
a transmitted sub-beam, comprising a first portion of the input
beam, passing through the etalon, and a reflected sub-beam,
comprising a second portion of the input beam, reflected at a first
variable angle of reflection from the etalon; a second arm
extending from the frame; a mirror positioned on the second arm for
receiving the reflected sub-beam at a second variable acute angle
of incidence for reflecting the reflected beam at a second variable
acute angle of reflection along an output path; a first output port
for receiving the transmitted sub-beam; and a second port for
receiving the reflected sub-beam; wherein rotation of the frame
about the rotation axis changes the first variable acute angle of
incidence, thereby enabling the first portion of the input beam to
be adjusted to between 0% and 90% of the input beam, and the second
portion of the input beam to be adjusted to between 10% and 100% of
the input beam.
2. The beamsplitter according to claim 1, wherein the first arm is
mounted at a fixed angle relative to the second arm, whereby the
output path is fixed relative to the input path.
3. The beamsplitter according to claim 2, wherein the fixed angle
is 45.degree., and wherein the output path is perpendicular to the
input path.
4. The beamsplitter according to claim 3, wherein the first
variable acute angle of incidence, the first variable angle of
reflection, the second variable angle of incidence, and the second
variable angle of reflection add up to 90.degree. for each of the
first variable acute angles of incidence.
5. The beamsplitter according to claim 1, wherein the frame is
rotatable, whereby the first variable acute angle of incidence is
variable between 0.degree. and 20.degree..
6. The beamsplitter according to claim 1, further comprising a
mount for supporting the frame, wherein the mount comprises a base
and a tilting stage pivotable relative to the base for adjusting an
angular position of the first arm, and thereby adjusting the first
variable acute angle of incidence.
7. The beamsplitter according to claim 1, wherein the etalon is
between 1 um and 1 mm thick.
8. The beamsplitter according to claim 1, wherein the etalon
comprises a solid etalon between 20 um and 1 mm thick.
9. The beamsplitter according to claim 8, wherein the etalon
comprises parallel uncoated faces, each having a reflectivity of
between 3% to 36%.
10. The beamsplitter according to claim 8, wherein the etalon
comprises parallel coated faces, each having a reflectivity of
between and 5% to 65%.
11. The beamsplitter according to claim 8, wherein the etalon
comprises parallel coated faces, each having a reflectivity of
between and 55% to 65%.
12. The beamsplitter according to claim 1, wherein the etalon
comprises a solid etalon between 50 um and 400 um thick with an
index of refraction of greater than 1.3 @ 550 nm,
13. The beamsplitter according to claim 12, wherein the etalon is
comprised of a material selected from the group consisting of fused
silica, sapphire, ZnSe, and suitable optical glass.
14. The beamsplitter according to claim 1, wherein the mirror has a
reflectivity of substantially about 99% to 100%.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present invention claims priority from U.S. Patent
Application No. 61/380,840 filed Sep. 8, 2010, which is
incorporated herein by reference for all purposes.
TECHNICAL FIELD
[0002] The present invention relates to a beamsplitter, which has
properties that vary with the input angle, and in particular to a
rotating optical component for adjusting the incident angle on the
optical component, and therefore the beamsplitting ratio, while
maintaining the input and output angles constant.
BACKGROUND OF THE INVENTION
[0003] Frequently, in the optics industry, there is a need for
custom beam splitters, which can split a given wavelength into
sub-beams at given percentages, e.g. a 30%/70%
reflective/transmissive beam splitter for 532 nm light. A custom
beam splitter can cost $3,000 for a very simple flat plate beam
splitter up to $12,000 for more complex cube beam splitters.
Unfortunately, the conventional custom beam splitters are only
designed one splitting percentage and a small range of
wavelengths.
[0004] U.S. Pat. No. 6,084,717 issued Jul. 4, 2000 to Wood et al,
discloses a laser beam splitter, in which plate beam splitters,
designed for a specific wavelength and a specific splitting ratio,
are used to divide an input beam into eight equal output beams by
passing sub-beams in sequence through the plate beam splitters to
obtain the desired output ratio.
[0005] Similarly, U.S. Pat. No. 5,798,867 issued Aug. 25, 1998 to
Uchida et al, discloses a laser beam splitter, in which a beam
splitter plate with a coating that varies along its length, is
laterally adjustable to adjust the beam splitting ratio. Again, the
coating is designed for a certain wavelength of input light and a
certain angle of incidence.
[0006] U.S. Pat. No. 6,678,447 relates to a polarization beam
splitter, which requires a plurality of modules that have to be
added, rotated and removed, as varying splitting ratios are
required. Furthermore the location of the output port is constantly
changing as the modules are rotated and removed.
[0007] Another polarization beam splitter is disclosed in U.S. Pat.
No 4,859,029 issued Aug. 22, 1989 to Durrell, requiring a high
angle of incidence and polarized light.
[0008] An object of the present invention is to overcome the
shortcomings of the prior art by providing a simple beam splitter
that can be adjusted to give any reflectivity between about 10% and
about 100% and a tranmsission that varies from about 0% to about
90% for any wavelength in the region of interest, e.g. visible, IR
etc.
[0009] Another object of the present invention is to provide a
variable beamsplitter in which the input and output port positions
are constant for all beamsplitting ratios.
SUMMARY OF THE INVENTION
[0010] Accordingly, the present invention relates to an optical
beam splitter comprising:
[0011] an input port for launching an input optical signal at a
first wavelength along an input path;
[0012] a frame rotatable about a rotation axis perpendicular to the
input path;
[0013] a first arm extending from the frame;
[0014] an etalon mounted on the first arm disposed in the input
path at a first variable acute angle of incidence, whereby the
input optical signal is split into a transmitted sub-beam,
comprising a first portion of the input beam, passing through the
etalon, and a reflected sub-beam, comprising a second portion of
the input beam, reflected at a first variable angle of reflection
from the etalon;
[0015] a second arm extending from the frame;
[0016] a mirror positioned on the second arm for receiving the
reflected sub-beam at a second variable acute angle of incidence
for reflecting the reflected beam at a second variable acute angle
of reflection along an output path;
[0017] a first output port for receiving the transmitted sub-beam;
and
[0018] a second port for receiving the reflected sub-beam;
[0019] wherein rotation of the frame about the rotation axis
changes the first variable acute angle of incidence, thereby
enabling the first portion to be adjusted to between 0% and 90% of
the input beam, and the second portion to be adjusted to between
10% and 100% of the input beam.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The invention will be described in greater detail with
reference to the accompanying drawings which represent preferred
embodiments thereof, wherein:
[0021] FIG. 1 is an isometric view of the beam splitter device of
the present invention;
[0022] FIG. 2 is an isometric view of the dual reflector structure
of the beam splitter device of FIG. 1;
[0023] FIGS. 3a, 3b and 3c illustrate the beam splitter of FIG. 2
at various tilt angles; and
[0024] FIG. 4 is a plot of the reflectivities vs. angular position
for 500 nm and 550 nm light.
DETAILED DESCRIPTION
[0025] With reference to FIGS. 1, 2 and 3a to 3c, the beam splitter
device of the present invention includes a fixed base 1, a
rotatable mount 2, and a dual reflector frame 3. The fixed base 1
includes an outer housing 4, and a rotating/sliding pedestal 6,
which can be rotated and extended vertically relative to the outer
housing 4. A rotating knob with a threaded rod 7 extends through
the fixed base 1 for locking the pedestal 6 in any desired angular
and vertical position relative to the outer housing 4. The
rotatable mount 2 is fixed on the outer free end of the pedestal 6
enabling the angular and vertical position of the rotatable mount 2
and of the dual reflector frame 3, to be adjusted accordingly.
Other suitable bases, which can substitute for the fixed base 2 and
rotatable mount 3, are within the scope of the invention
[0026] The rotatable mount 2 is comprised of a base 8, mounted on
the pedestal 6, and a tilting stage 9 pivotable relative to the
base 8 to provide relatively fine adjustments, e.g. 1.degree. to
20.degree., preferably 1.degree. to 10.degree., to the angular
position of the dual reflector frame 3. A first adjusting screw 11
extending through the base 8 pivots the tilting stage 9 about a
first lateral axis at one end of the rotatable mount 2. A second
adjusting screw 12, extending through the base 8, pivots the
tilting stage 9 about a second longitudinal axis, perpendicular to
the first axis.
[0027] The dual reflector frame 3 includes a first arm 13 for
supporting a mirror 14, and a second arm 16 for supporting an
etalon 17. Ideally, the first arm 13, i.e. the face of etalon 17,
is disposed at an angle of 45.degree. to the second arm 16, i.e.
the face of mirror 14, to ensure the reflected light beam R exits
at an output port, which is in a constant position, e.g. at an
angle perpendicular to the input beam; however, any acute angle is
possible depending on the desired output angle and position.
Typically, the mirror 14 is a standard mirror (polished) with
substantially about 99% to 100% reflectivity. The etalon 17 is
ideally very thin, e.g. 1 um to 1 mm thick, whereby at the thicker
end of the range, e.g. 20 um to 1 mm, it can be a solid etalon,
which is polished conventionally or using a fluid jet polishing
technique to obtain the required thickness. The solid etalon 17
could then be coated to obtain the desired reflectivity or left
uncoated for low reflectivity surfaces. For the visible and near IR
wavelength ranges the solid etalon is preferably between 50 um and
400 um with an index of refraction of greater than 1.3 @ 550 nm,
e.g. comprising fused silica (n=1.46), sapphire (n=1.76), ZnSe
(n=2.4) or other suitable optical glasses. For the thinner range of
thicknesses, e.g. 1 um to 15 um, optical coatings can be used to
obtain the required thickness and reflectivities.
[0028] Typical reflectivities for the front and rear parallel faces
of the etalon 17 are 3% to 36% each for uncoated materials, and 5%
to 65% each for coated material at the required wavelengths. Even
an uncoated etalon 17 made from optical glass, e.g. clear
homogenous glass of known refractive index, provides a good
response, e.g. about 15% variability. Preferably, the etalon 17
would have coatings of between 55% to 65%, and ideally 60%, on each
side and will provide the reflected sub-beam R any desired
percentage portion between about 10% and about 100% and the
transmitted sub-beam T with any desired percentage portion from
about 0% to about 90% for any wavelength in the region of interest,
e.g. visible, IR etc, as the angle of incidence on the etalon 17 is
adjusted.
[0029] The dual reflector frame 3 can have a custom mount to
provide the rotation about the pivot axis; however, a 1'' disk 19
can be mounted on the end of the frame 3, so that the frame 3 can
easily be mounted in the illustrated 1'' rotatable mount 2. The
frame 3 can also be mounted in a motorized structure and computer
controlled for more precise angular control and applications that
require automation.
[0030] With particular reference to FIGS. 3a to 3c, an incoming
beam 21 at a desired wavelength or wavelength range, launched from
input port 22, hits the etalon 17 at a predetermined acute angle of
incidence (.alpha..sub.i-e), e.g. 4.degree. for FIG. 3a, 6.degree.
for FIGS. 3b and 8.degree. for FIG. 3c, but preferably between
0.degree. and 20.degree., whereby the etalon 17 reflects a first
portion or percentage of the input beam 21, i.e. sub-beam R, and
transmits another portion or percentage of the input beam 21, i.e.
sub-beam T. The transmitted sub-beam T continues along the same
path as the input beam 21 to a first output port 23, while the
reflected sub-beam R is directed towards the mirror 14 at an angle
of reflection (.alpha..sub.r-e) equal to the angle of incidence
(.alpha..sub.i-e), e.g. 4.degree., 6.degree. or 8.degree. according
to FIG. 3a, 3b or 3c. The first output port 23 can be a fixed
structural element, e.g. with a lens etc. or simply a fixed
position in which another optical element is disposed to receive
the reflected sub-beam R. The mirror 14 re-directs the sub-beam R
along a predetermined output path, e.g. perpendicular to the input
beam 21, dependent upon the angle between the first and second arms
13 and 16 to a second output port 24. The second output port 24 can
be a fixed structural element, e.g. with a lens etc. or simply a
fixed position in which another optical element is disposed to
receive the transmitted sub-beam T. Because the first and second
arms 14 and 16, respectively, are 45.degree. apart in the
illustrated embodiment, the angle of incidence (.alpha..sub.i-m) on
the mirror 16 is 45.degree. minus the angle of reflection
(.alpha..sub.r-e) from the etalon 17, e.g.
45.degree.-4.degree.=41.degree., which is also equal to the angle
of reflection (.alpha..sub.r-m) of the reflected sub-beam R from
the mirror 14. Accordingly, the output path for the reflected
sub-beam R is perpendicular to the path of the input beam 21, e.g.
41.degree. (.alpha..sub.i-m)+41.degree. (.alpha..sub.r-m)+4.degree.
(.alpha..sub.i-e)+4.degree. (.alpha..sub.r-e)=90.degree. The angle
of incidence of the input beam 21 on the etalon 17 is adjusted by
rotating the dual reflector frame 3 via the tilting stage 9, using
the first adjusting screw 11 or other suitable means. As the dual
reflector frame 3 rotates, the reflectivity of the etalon 17, at
any given wavelength of the input beam 21 traveling along the input
path, will vary rapidly, but the output direction of the reflected
beam R always remains at a relatively constant angle, e.g.
90.degree. to the input beam 21, because as the angle of incidence
(.alpha..sub.i-e) (and reflection (.alpha..sub.r-e)) on the etalon
17 increase, the angle of incidence (.alpha..sub.i-m) (and
reflection (.alpha..sub.r-m)) on the mirror 14 decreases
accordingly. As seen in FIGS. 3b and 3c, if the angle of incidence
(.alpha..sub.i-e) on the etalon 17 is increased to 6.degree. or
8.degree., respectively, the corresponding angles of incidence
(.alpha..sub.i-m) on the mirror 14 decrease to 39.degree. and
37.degree., respectively, wherein the angle of incidence
(.alpha..sub.i-e) on the etalon 17, the angle of reflection
(.alpha..sub.r-e) on the etalon 17, the angle of incidence
(.alpha..sub.i-m) on the mirror 14 and the angle of reflection
(.alpha..sub.r-m) on the mirror 14 always adds up to 90.degree. for
every angle of incidence (.alpha..sub.i-e) on the etalon 17,
thereby ensuring that the output path is perpendicular to the input
path at all angles of incidence (.alpha..sub.i-e), and that the
position of the first and second output ports 23 and 24 remain
constant. The transmitted beam T has a very small parallel shift
due to the thickness of the etalon 17, e.g. typically about 5
micron or less. Increasing or decreasing the angle between the
first and second arms 13 and 16 would corresponding increase or
decrease the angle between the input and output paths by twice as
much.
[0031] As the dual reflector frame 3 is tilted about the lateral
axis perpendicular to the input and output paths, to vary the angle
of incidence of the input beam 21 on the etalon 17, the response of
the etalon 17 shifts providing a range of reflectivity for each
wavelength. FIG. 4 illustrates the transmission curves of two
wavelengths, i.e. 500 nm and 550 nm, which plots transmission, 0%
to 90%, versus a variety of angles 0.degree. to 20.degree.. The
reflectivities cycle from minimum to maximum, repeating every few
degrees of incident angle; however, the smaller the angle, the
flatter the slope of the transmission curve, thereby providing
somewhat more control at low incident angles, e.g. <6.degree.,
than the higher angles, e.g. >20.degree..
[0032] The reflectivity of the etalon 17 varies rapidly with
wavelength; accordingly, the present invention works best for
relatively narrow wavelength range sources that are collimated
(lasers).
[0033] The scope of the invention can be broadened to include other
optics instead of the etalon 17, e.g. any optical element with
properties that vary with angle, mounted at a fixed angle to the
mirror 14. Other types of coated or uncoated optical elements might
also be used, waveplates, dispersion compensators, polarizers
etc.
* * * * *